A fuel filter of the above type typically comprises a fuel inlet and outlet, and in a fuel supply circuit for a diesel engine allows filtering the diesel fuel to remove impurities. The additive tank is housed in the filter housing and contains a liquid additive, for improving fuel quality and in particular fuel distribution in the engine, engine performance, engine stability during operation, and/or for facilitating the regeneration of the particulate filter. This type of liquid additive is typically useful for improving engine durability. Document WO 2012/104552 describes such a filter type, and non-limiting examples of liquid additives are provided at the end of the description in that document.
It is advantageous to be able to dispense the liquid additive without requiring high-precision metering pumps or managing an associated calculator, in order to reduce the cost of the additive dispensing device.
One advantage of the dispensing mode described in document WO 2012/104552 is the ability to extend the service period of the additive tank by limiting or even stopping the supply of additive in order to prevent, under certain conditions, excessive concentration of additive in the fuel. It also optimizes the concentration of additive in the fuel in order to find a compromise between the amount that is necessary and sufficient, and an excessive concentration which can reduce the service period of the additive tank and/or have a negative impact on other vehicle elements, such as clogging the particulate filter. For this purpose, the liquid additive is released by the effect of a pressure difference, the additive being placed in an inner flexible bag or casing with a fluidtight movable wall and being at the same pressure as the fuel placed in an outer casing of the additive chamber. Typically, the pressure difference can result from positive pressure exerted by the fuel or negative pressure near a dispensing port for the additive liquid.
An assembly combining a filter element and an additive chamber is relatively complex to assembly, however, especially if one wants this assembly to form a removable cartridge that is replaced as one piece. It is therefore difficult, for the user or operator performing the replacement, to disconnect/connect such a fuel circuit cartridge, particularly for the following reasons:                connection to the dispensing circuit must be done with precision and as simply and quickly as possible;        contact between the user's skin and the liquid additive contained in the tank may be hazardous for the user.        
In document WO 2012/104552, it is required that the additive tank be arranged inside a removable external cartridge housing that is typically at the base of the external housing. There is then a loss of flexibility in the filter architecture, to the extent that attachment of the filter under the hood must be done with a filter head (cover).
A type of spin-on cartridge incorporating an additive dispensing function is known from document US 2009/0206024 A1. In this case, there is again a loss of flexibility in the filter architecture. In addition, the method of dispensing by progressive deformation of a heat sensitive material does not prevent leakage of liquid additive, which can hazardous to a user performing a replacement operation.